Nickel plating



Aug. 8, 1967 5 g, JR" ET AL 3,335,027

' NICKEL PLATING Filed July 17, 1964 AP, mm EFFECT OF CARBON D/SULF/DE Fo 20 CONCENTRATION o/v REACT/0N WITH 25mm /w (0014 AT 25% 1 I0 I 229% O45 l0 I5 so 4' o CARBON D/SULF/DE, VOLUME 4o Fl 2 REACT/0N RA rEs 0F25mm gm? /w (0024 WITH VARIOUS CONCENTRATIONS 3 OF CARBON D/SULF/DE AT25 0 2o 5AM. H. PITTS Jr.

5 MILTON A. THOMPSON INVENTORS 5 IO :5 2o 25 BY TIME, MINUTES A T'TORNEYUnited States Patent 3,335,027 NICKEL PLATING Sam H. Pitts, Jr., Arvada,and Milton A. Thompson,

Boulder, Colo., assignors to the United States of America as representedby the United States Atomic Energy Commission Filed July 17, 1964, Ser.No. 383,533 Claims. (Cl. 117-107.2)

ABSTRACT OF THE DISCLOSURE A nickel carbonyl plating process andresulting coating, wherein vapor of Ni(CO) and CS may provide coatingsat room temperatures.

The present invention relates to nickel plating, and more particularlyto a new and improved method of vapor plating with nickel carbonyl, andto the nickel coating produced thereby.

While the utilization of nickel carbonyl 'gas or vapor (actually nickeltetracarbonyl, Ni(CO) decomposition to form nickel coatings or platingspossess a number of advantages over other methods, there have beenobjections to its employment. For example, in some instances its use isdeemed unsatisfactory due to relatively high temperatures required toobtain decomposition, which temperatures may damage, destroy orotherwise objectionably affect the article to be plated. Thistemperature difli why has been reduced by mixing with the Ni(CO) aquantity of hydrogen monosulphide (-H S), which appreciably lowers thedecomposition temperature. However, the decomposition temperature hasstill been excessive for some uses and it has been attempted to lowerthe Ni(CO) decomposition temperature by addition of oxygen or watervapor (0 or H O vapor) to the Ni(CO) -H S mixture, but this introducesthe complication of requiring a third constituent and controlling meanstherefor and, further, platings or coatings formed by employing amixture of H 8 and Ni(CO) have been found to lack optimum physicalcharacteristics.

The present invention aims to overcome or minimize the above and otherdifficulties by providing a new vapor mixture, namely, Ni(CO) and carbondisulfide (CS and method to plate surfaces with highly improvedcoatings, all without the necessity of employing higher than ordinaryroom temperatures.

An object of the present invention is to provide improvements in nickelplating.

Another object of the invention is to provide improvements in nickelplating operative at room temperatures.

Another object of the invention is to provide nickel platingimprovements which furnish enhanced nickel coatings.

Still another object of the invention is to provide improved nickelcoatings of greater thickness.

A still further object of the invention is to provide a nickel coatingmethod which is faster than previous methods and in which there isobtained more efiicient utilization of Ni(CO) A still further object ofthe present invention is to provide nickel coating improvements whereinaccumulation of by-products has little or no objectionable effect.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiments about to be described, orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the invention in practice.

The embodiments of the invention illustrated or described are notintended to be exhaustive nor to limit the 3,335,027 Patented Aug. 8,1967 invention to the precise forms disclosed, but are chosen in orderto best explain the principles of the invention and their application inpractical use to thereby enable others skilled in the art to bestutilize the invention in various embodiments 'and modifications as arebest adapted to the particular use contemplated.

In the accompanying drawing:

FIG. 1 is a largely diagrammatic representation of apparatus that may beemployed to perform the process;

FIG. 2 is a graphical representation illustrating the effect of variousCS concentrations in reaction with Ni-(CO) and FIG. 3 is a graphicalrepresentation illustrating re-action rates of Ni(CO) with variousconcentrations of CS Stated briefly, in investigating disadvantages ofprevious nickel carbonyl plating methods, compositions, and resultingplatings it was discovered that a mixture of CS gas or vapor with Ni(CO)gas or vapor provided, at room temperatures (around 20 C. to 30 0.),rapid decomposition of Ni(CO) and very desirable nickel coatings on thesurfaces of objects.

Any appropriate apparatus may be utilized in carrying out the process.By way of example, and with reference to FIG. 1, a bell jar or reactionvessel 2 may be sealed against an O-ring to a stainless steel base plate4, which is in turn fitted with suitable conduit connections forevacuation of the vessel and for gas chargings thereinto. The reactionvessel may be clamped down against the ring or retained by externalatmospheric pressure, as desired, dependent upon pressures within thevessel. A motor driven fan or magnetic electric stirrer (not shown) maybe provided, if desired, to facilitate gas or vapor mixing in thevessel, and pressure measuring equipment such as a mercury manometer 5may communicate with the interior of the vessel. An object or objectswith surfaces to be plated is placed inside the vessel. After evacuationof air from the vessel by a vent conduit 7, CS may be admitted orcharged therein via a conduit 8 and control valve from a supply flask orbottle 10 and thereafter the Ni(CO) gas through another conduit 11 andcontrol valve from another flask or bottle 12. Because of the toxicnature of Ni(CO) care should be taken in handling it and hence it may bedesired to enclose the entire system in a hood (not shown) which hasappreciable air flow therethrough, and to connect an evacuation conduit13 from the vessel to a heated (e.g., by an electrical heating tape 9)decomposition chamber 14 filled with Pyrex glass beads and a filter 15filled with glass Wool, both the chamber and filter being interposedbetween the ves sel and the vessel evacuation pump 16 so that vaporleaving the vessel passes through the decomposition chamber and filter.

In decomposition, the mixtures of CS and Ni(CO).; appear to effect apressure increase in the range of about one to 2.5 times that of theinitial mixture. Hence the decomposition reaction may generally beobserved by noting pressure changes within the vessel and graphicallyrepresented by plotting pressure against time. In some specializedcase-s, e.-g., in the plating of finely divided particulate matter, thepressure may be about one times that of the Ni(CO) charge even thoughinfrared analysis shows complete Ni(CO) conversion; usually however, on

'objects with less surface area, pressure increase is about conversionof Ni(CO) when 13 to 15 or higher volume percent CS is employed down tono reaction as the CS concentration reaches esentially zero (see FIG.2). Higher CS concentrations are not detrimental to decomposition orconversion of Ni(CO) but do not appear to be particularly advantageous.

The quantity of Ni(CO) is not critical, but for safety reasons,limitations of equipment should be considered. The equipment shouldwithstand a minimum pressure increase of about 2.5 times the Ni(CO)charge. In a bell jar system with only external atmospheric pressureholding down the jar or vessel, the maximum Ni(CO) charge should,'ofcourse, be such that any subsequent internal pressure increases will beless than the external atmospheric pressure, in order that the vesselnot be released.

Up to about 6% to 7% water vapor or 18% air, by volume, in the vreactionmixture appear to have no promoting effect on the decompositionreaction.

In FIG. 2 the curve illustrates the effect of CS concentrations upon thereaction of Ni(CO) with an initial pressure of 25 mm. of mercury, inabout a one liter capacity reaction vessel and at a room temperature ofabout 25 C. The ordinate shows pressure increase, this being anindicator of conversion of Ni(CO) to nickel and CO. It may be noted thatfrom zero CS concentration the curve slopes upwardly to level off ataround 16% to 18% CS by volume, thus showing that adding greater amountsof CS does not appreciably increase the pressure, and hence the nickelyield. There is nothing critical in the 25 mm. Ni(CO) pressure referredto in connection with FIGS. 2 and 3, this being used merely asexemplary; the reaction and method work just as well at other convenientpressures.

FIG. 3 shows the effect of various concentrations of CS on the reactionrate of Ni(CO) initial pressure of the latter being 25 mm. of mercury,as in FIG. 2.

When employing Ni(CO) at anywhere from around 20 mm. to 50 mm. ofmercury in an evacuated vessel and a concentration of CS around 13% to15% by volume, infrared spectrographic analyses of residual gasindicates that essentially all the CS is consumed and that there isobtained about a 98% to 100% conversion of Ni(CO) By way of comparison,based upon observed pressure change and the theoretical 1 to 4 volumeincrease for decomposition of Ni(CO) and with H S reactions employing100 mm. of Ni(CO)., and reaction times two to three times longer thanfor the CS reactions, H S with Ni(CO) has been found to give only about2% to conversion.

Another major improvement by use of CS with Ni(CO) as compared with H 8is that with the former, accumulation of by-products, e.g., CO, has noappreciable objectionable elfect on the reaction; the reaction goes tocompletion without hindrance, whereas with the latter, accumulation ofCO is a reaction-governing step that causes a retardation of plating.With CS -Ni(CO) vapor, the nickel formation occurs rapidly, the majorityof the reaction occurring within as little as one to four minutes.

Nickel coatings or platings may be built up by admitting successivequantities or passes of CS and Ni(CO) to a reaction vessel until adesired cumulative thickness is obtained on an object. It has beenfound, by

interferometric thickness measurements, that with the presentimprovement, plating thicknesses three to four times greater areobtained by use of CS as compared with use of H 8, a single layerthickness from the CS mixture reaction lying in the range of 1700 to2100 Angstroms using 25 mm. Ni(CO) in a 1-liter system, as compared Withonly from about 400 to 600 Angstroms obtained by the H 8 mixture.

With the CS mixture, eight to ten layers of nickel may be successivelyapplied without evidence of peeling, whereas with the H 8 mixture thenickel has been found brittle, with cracking and peeling occurring afterdeposit of only two or three nickel layers. Metallic plating from the CSreaction analyses about 80% to 82% nickel, the balance being made up ofsulphur, carbon, hydrogen, and oxygen.

The mechanism of the reaction between the CS and Ni(CO) in a vapormixture is not wholly understood; but it is currently thought that a newcomplex is formed. It does not appear to be entirely of catalyticnature, but whatever it may be the nickel pl-atings and results achievedby mixtures of CS and Ni(CO) vapors are greatly superior to thoseresulting from previously known mixtures.

It will be seen that the present invention provides a new and improvedmethod of obtaining nickel coatings or films, as well as greatlyimproved nickel coatings themselves. The method is relatively simple,rapid, makes more eflicient use of Ni(CO) than heretofore, and may beeffected at room temperatures.

As various changes may be made in the form, construction and arrangementof the parts herein without departing from the spirit and scope of theinvention and without sacrificing any of its advantages, it is to beunderstood that all matter herein is to be interpreted as illustrativeand not in a limiting sense.

We claim:

1. The method of nickel plating a surface of an object comprisingexposing said surface to a vapor of Ni(CO) and CS 2. The method asclaimed in claim 1, wherein temperature of vapor is from about 20 C. toabout 30 C.

3. The method as claimed in claim 1, wherein said CS comprises about 13%to 15% by volume of said vapor.

4. The method as claimed in claim 1, wherein said Ni(CO) is at aninitial pressure of from about 20 to 50 millimeters of mercury.

5. An improved object having a surface coated with a plurality of layersof nickel by the process of claim 1, and wherein said layers are ofenhanced adherence and resistant to peeling and cracking.

References Cited UNITED STATES PATENTS 2,798,051 7/1957 Bicek 117107.2 X2,881,094 4/1959 Hoover 117l07.2 2,886,468 5/1959 Hoover et al. 117107.22,921,871 1/1960 Cummins 117107.2 X 3,086,881 4/1963 Jenkin l17l07.2 X

ALFRED L. LEAVITT, Primary Examiner. A. GOLIAN, Assistant Examiner.

1. THE METHOD OF NICKEL PLATING A SURFACE OF AN OBJECT COMPRISINGEXPOSING SAID SURFACE TO A VAPOR OF NI(CO)4 AND CS2.